My single biggest beef about PG is the lack of query planner hints.

Unplanned query plan changes as data distribution shifts can and does cause queries to perform orders of magnitude worse. Queries that used to execute in milliseconds can start taking minutes without warning.

Even the ability to freeze query plans would be useful, independent of query hints. In practice, I've used CTEs to force query evaluation order. I've considered implementing a query interceptor which converts comments into before/after per-connection settings tweaks, like turning off sequential scan (a big culprit for performance regressions, when PG decides to do a sequential scan of a big table rather than believe an inner join is actually sparse and will be a more effective filter).

Take a look at this Postgres Extension: http://pghintplan.osdn.jp/pg_hint_plan.html

I am even using this with AWS RDS since it comes in the set of default extensions that can be activated.

I recently put up a PR for a README, you can read it here: https://github.com/ossc-db/pg_hint_plan/blob/8a00e70c387fc07...